This invention relates to an ink jet recording head wherein a piezoelectric element is formed via a diaphragm in a part of each of pressure generating chambers communicating with nozzle openings for jetting ink drops and ink drops are jetted by displacement of the piezoelectric element, and an ink jet recording apparatus comprising the ink jet recording head.
The following two types of ink jet recording heads, each wherein a part of a pressure generating chamber communicating with a nozzle opening for jetting an ink drop is formed of a diaphragm and the diaphragm is deformed by a piezoelectric element for pressurizing ink in the pressure generating chamber for jetting an ink drop through the nozzle opening, are commercially practical: One uses a piezoelectric actuator in a vertical vibration mode in which the piezoelectric element is expanded and contracted axially and the other uses a piezoelectric actuator in a deflection vibration mode.
With the former, the volume of the pressure generating chamber can be changed by abutting an end face of the piezoelectric element against the diaphragm and a head appropriate for high-density printing can be manufactured, but a difficult step of dividing the piezoelectric element like comb teeth matching the arrangement pitch of the nozzle openings and work of positioning and fixing the piezoelectric element divisions in the pressure generating chambers are required and the manufacturing process is complicated.
In contrast, with the latter, the piezoelectric element can be created and attached to the diaphragm by executing a comparatively simple process of putting a green sheet of a piezoelectric material matching the form of the pressure generating chamber and baking it, but a reasonable area is required because deflection vibration is used; high-density arrangement is difficult to make.
On the other hand, to solve the problem of the latter recording head, Japanese Patent Publication No. 5-286131A proposes an art wherein an uniform piezoelectric material layer is formed over the entire surface of a diaphragm according to a film formation technique and is divided to a form corresponding to a pressure generating chamber according to a lithography technique for forming a piezoelectric element separately for each pressure generating chamber.
This eliminates the need for work of putting the piezoelectric element on the diaphragm and the piezoelectric element can be created by the lithography method, an accurate and simple technique. In addition, the piezoelectric element can be thinned and high-speed drive is enabled.
However, in the manufacturing method according to the thin-film technique and the lithography method described above, after thin film patterning, pressure generating chambers are formed. At the time, a diaphragm is deflected to the pressure generating chamber side by the effect of relaxation of the internal stresses in an upper electrode and piezoelectric layers and the deflection remains as the initial deformation of the diaphragm.
Further, in a piezoelectric vibrator manufactured by the thin-film technique and the lithography method, in which arm portions of a lower electrode are removed by the patterning, a piezoelectric layer becomes thinner. Thus, the strength of the dielectric breakdown on both sidewalls in width direction of the lower electrode becomes lower and thereby the dielectric breakdown occurs easily.
It is therefore an object of the present invention to provide an ink jet recording head, wherein the dielectric breakdown of the piezoelectric layer is prevented and wherein the initial deflection amount of a diaphragm is decreased, and an ink jet recording apparatus comprising the ink jet recording head.
In order to achieve the above object, according to a first aspect of the present invention, there is provided an ink jet recording head comprising: a pressure generating chamber communicating with a nozzle opening; and a piezoelectric element a lower electrode provided on an area facing the pressure generating chamber via an insulating layer, a piezoelectric layer provided on the lower electrode, and an upper electrode provided on the piezoelectric layer, wherein at least both ends of the lower electrode in a width direction thereof are positioned within the area facing the pressure generating chamber, and the piezoelectric layer covers sides of both ends of the lower electrode in the width direction thereof.
In the first aspect, the both side wall of the lower electrode in the width direction thereof patterned in the pressure generating chamber are covered with the piezoelectric layer, thus the strength of the dielectric breakdown thereon is improved and the insulating layer and the piezoelectric layer are brought into intimate contact with each other, whereby the initial deflection amount of a diaphragm is decreased.
According to a second aspect of the present invention, in the ink jet recording head of the first aspect, crystal direction of the piezoelectric layer is preferentially oriented.
In the second aspect, the piezoelectric layer is formed in a thin film process, so that crystal is preferentially oriented.
According to a third aspect of the present invention, in the ink jet recording head of the second aspect, the piezoelectric layer has a columnar crystal structure.
In the third aspect, the piezoelectric layer is formed in a thin film process, so that the piezoelectric layer has a columnar crystal structure.
According to a fourth aspect of the present invention, in the ink jet recording head of the first to third aspect, the insulating layer in the area under the area where the lower electrode is formed is thicker than any other area.
In the fourth aspect, the piezoelectric layer is at a position distant from the neutral axis of bend caused by drive of the piezoelectric element, so that displacement efficiency is improved.
According to a fifth aspect of the present invention, in the ink jet recording head of any of the first to fourth aspects, the top of the insulating layer in a thickness direction thereof is made of an adhesive insulating layer made of a material having a good adhesion with the piezoelectric layer. The adhesive insulating layer is adhered with the piezoelectric layer covering sides of both ends of the lower electrode in the width direction thereof.
In the fifth aspect, the lower electrode in the area facing the pressure generating chamber is covered completely with the piezoelectric layer and the strength of the dielectric breakdown on the sidewall is furthermore improved.
According to a sixth aspect of the present invention, in the ink jet recording head of the fifth aspect, the material of the adhesive insulating layer is made of either one of an oxide or a nitride of at least one element selected from composite element of the piezoelectric layer.
In the sixth aspect, the intimate contact property between the insulating layer and the piezoelectric layer is improved.
According to a seventh aspect of the present invention, in the ink jet recording head of the sixth aspect, the adhesive insulating layer is made of zirconium oxide.
In the seventh aspect, the rigidity of the insulating layer is improved and the durability is enhanced.
According to an eighth aspect of the present invention, in the ink jet recording head of any of the fifth to seventh aspects, the insulating layer is made of the adhesive insulating layer.
In the eighth aspect, the insulating layer is formed easily and the manufacturing process is simplified.
According to a ninth of the present invention, in the ink jet recording head of the eighth aspect, the insulating layer is formed directly on a silicon monocrystalline substrate.
In the ninth aspect, the zirconium oxide film shows sufficient durability even solely.
According to a tenth aspect of the present invention, in the ink jet recording head of the eighth aspect, the insulating layer is formed on a silicon dioxide film formed on the silicon monocrystalline substrate. The portions of the silicon dioxide film corresponding to the pressure generating chambers are removed.
In the tenth aspect, the displacement efficiency of an actuator can be enhanced.
According to an eleventh aspect of the present invention, in the ink jet recording head of any of the fifth to tenth aspects, the piezoelectric layer is made of PZT and the adhesive insulating layer is made of zirconium oxide.
In the eleventh aspect, the intimate contact property between the piezoelectric layer and the insulating film is improved.
According to a twelfth aspect of the present invention, in the ink jet recording head of any of the first to eleventh aspects, both ends of the piezoelectric layer in a width direction thereof are positioned in the area facing the pressure generating chamber.
In the twelfth aspect, the areas corresponding to both sides in the width direction the pressure generating chamber become thin, so that the displacement amount of the diaphragm is increased.
According to a thirteenth aspect of the present invention, in the ink jet recording head of any of the first to eleventh aspects, the piezoelectric layer is extended to the areas corresponding to peripheral walls on both sides in the width direction of the pressure generating chamber and the piezoelectric layer on the lower electrode is thicker than any other area.
In the thirteenth aspect, the lower electrode is covered with the piezoelectric layer reliably, so that the strength of the dielectric breakdown on the sidewall is improved and the strength is also increased. Since the end of the piezoelectric layer does not exist in the arm part, initial failure is avoided and durability is also improved.
According to a fourteenth aspect of the present invention, in the ink jet recording head of any of the first to eleventh aspects, the relationship among width WTE of the upper electrode, width WBE of the lower electrode, and thickness T of the piezoelectric layer satisfies:
(WBExe2x88x925T) less than WTE less than (WBE+5T).
In the fourteenth aspect, the piezoelectric layer sandwiched between the upper and lower electrodes is driven effectively.
According to a fifteenth aspect of the present invention, in the ink jet recording head of any of the first to fourteenth aspects, wherein the end of the lower electrode is disposed at one end portion in a longitudinal direction of the pressure generating chamber. The piezoelectric layer and the upper electrode are extended to the outside of the end of the lower electrode in the longitudinal direction of the pressure generating chamber. The end of the lower electrode constitutes one end of a piezoelectric active part which is a substantial driving part of the piezoelectric layer.
In the fifteenth aspect, dielectric breakdown of the piezoelectric layer is prevented without interfering with drive of the piezoelectric active part.
According to a sixteenth aspect of the present invention, in the ink jet recording head of the fifteenth aspect, the end of the piezoelectric active part is positioned inside from the peripheral wall of the pressure generating chamber.
In the sixteenth aspect, dielectric breakdown of the piezoelectric layer is prevented without interfering with drive of the piezoelectric active part.
According to a seventeenth aspect of the present invention, in the ink jet recording head of any of the first to fourteenth aspects, the end of the lower electrode is disposed at one end portion in a longitudinal direction of the pressure generating chamber. An end of the upper electrode is disposed inside from the end of the lower electrode in the longitudinal direction of the pressure generating chamber. The piezoelectric layer is extended to the outside of the end of the lower electrode in the longitudinal direction of the pressure generating chamber. The end of the upper electrode constitutes one end of a piezoelectric active part which is a substantial drive part of the piezoelectric layer.
In the seventeenth aspect, a distance can be kept between the end of the piezoelectric active part and the end of the lower electrode and dielectric breakdown caused by concentration of electric field, etc., at the end of in the longitudinal direction of the piezoelectric active part is prevented.
According to an eighteenth aspect of the present invention, in the ink jet recording head of any of the fifteenth to seventeenth aspects, a discontinuous lower electrode film discontinuous with the lower electrode is provided in an area facing the boundary between an end and peripheral wall of the pressure generating chamber.
In the eighteenth aspect, the rigidity of the diaphragm in the portion where the piezoelectric layer and the upper electrode are drawn to the area outside the pressure generating chamber is held high and destruction of the diaphragm and the piezoelectric layer in the portion is prevented.
According to a nineteenth aspect of the present invention, in the ink jet recording head of the eighteenth aspect, a wiring lower electrode which is made discontinuous with the discontinuous lower electrode and is connected at one end to external wiring is provided for each piezoelectric element.
In the nineteenth aspect, wiring can be drawn easily and efficiently from the piezoelectric active part.
According to a twentieth aspect of the present invention, in the ink jet recording head of any of the fifteenth to eighteenth aspects, the lower electrode is extended from an opposite end of the piezoelectric active part to the top of the peripheral wall of the pressure generating chamber.
In the twentieth aspect, the piezoelectric elements can be wired easily.
According to a twenty-first aspect of the present invention, in the ink jet recording head of the twentieth aspect, the lower electrode has a wider part at least wider than the pressure generating chamber in an area facing the proximity of one end of the pressure generating chamber and the wider part is extended from the end in the longitudinal direction of the pressure generating chamber to the top of the peripheral wall.
In the twenty-first aspect, the rigidity of the diaphragm in the proximity of the end of the pressure generating chamber is increased and durability is improved.
According to a twenty-second aspect of the present invention, in the ink jet recording head of any of the first to twenty-first aspects, the piezoelectric layer, and one of the upper electrode and a lead electrode connected onto the upper electrode are extended from the longitudinal direction of the area facing the pressure generating chamber to the outside thereof.
In the twenty-second aspect, the connection part of the upper electrode and external wiring can be formed easily in the area facing the peripheral wall of the pressure generating chamber.
According to a twenty-third aspect of the present invention, in the ink jet recording head of the twenty-second aspect, the direction that the lower electrode extends to the top of the peripheral wall differs from the direction that the piezoelectric layer, and one of the upper electrode and the load electrode connected onto the upper electrode extend to the top of the peripheral wall.
In the twenty-third aspect, the piezoelectric active part driven by applying a voltage exists in the area facing the pressure generating chamber and wiring can be drawn easily without requiring an inter-layer insulating film or a contact hole.
According to a twenty-fourth aspect of the present invention, in the ink jet recording head of the twenty-second aspect, the direction that the lower electrode extends to the top of the peripheral wall is the same as the direction that the piezoelectric layer, and one of the upper electrode and the lead electrode connected onto the upper electrode extend to the top of the peripheral wall.
In the twenty-fourth aspect, wiring can be drawn easily without requiring an inter-layer insulating film or a contact hole.
According to a twenty-fifth aspect of the present invention, in the ink jet recording head of the twenty-third or twenty-fourth aspect, either one of the lower electrode or the upper electrode is a common electrode.
In the twenty-fifth aspect, the piezoelectric elements can be wired easily.
According to a twenty-sixth aspect of the present invention, in the ink jet recording head of any of the first to twentieth aspects, the lower electrode is extended from the proximity of at least one end portion in a longitudinal direction of the area facing the pressure generating chamber to the outside in the width direction to form a common electrode.
In the twenty-sixth aspect, wiring can be drawn easily without requiring an inter-layer insulating film or a contact hole.
According to a twenty-seventh aspect of the present invention, in the ink jet recording head of any of the first to twenty-sixth aspects, the piezoelectric layer and the upper electrode are patterned in batch.
In the twenty-seventh aspect, the piezoelectric elements can be formed comparatively easily and the manufacturing process is simplified.
According to a twenty-eighth aspect of the present invention, in the ink jet recording head of any of the first to twenty-first aspects, both ends of the piezoelectric layer in the longitudinal direction thereof are patterned so as to be in the areas facing the pressure generating chambers and the upper electrode is continuously formed so as to cross the pressure generating chambers crossing in the width direction to form a common electrode.
In the twenty-eighth aspect, wiring can be drawn easily without requiring an inter-layer insulating film or a contact hole.
According to a twenty-ninth aspect of the present invention, in the ink jet recording head of any of the first to twenty-seventh aspects, a remaining part made of the same layer as the lower electrode is provided on tops of partitions on both sides in the width direction of the pressure generating chamber.
In the twenty-ninth aspect, the lower electrode removal area lessens, so that the piezoelectric layer is formed on the patterned lower electrode in a substantially uniform film thickness.
According to a thirtieth aspect of the present invention, in the ink jet recording head of the twenty-ninth aspect, a discontinuous lower electrode discontinuous with the lower electrode is provided on the outside of one end portion of the piezoelectric active part and the remaining part is extended continuously from the discontinuous lower electrode.
In the thirtieth aspect, the spacing between the lower electrode making up a part of the piezoelectric element and the remaining part can be made narrow and the piezoelectric layer is formed in a uniform film thickness more reliably.
According to a thirty-first aspect of the present invention, in the ink jet recording head of the twenty-ninth aspect, the remaining part is provided continuously with the lower electrode forming a part of the piezoelectric element.
In the thirty-first aspect, the spacing between the lower electrode making up a part of the piezoelectric element and the remaining part can be made comparatively narrow and the piezoelectric layer is formed in a uniform film thickness.
According to a thirty-second aspect of the present invention, in the ink jet recording head of any of the twenty-ninth to thirty-first aspects, the spacing between an end face in the width direction of the lower electrode and an end face in a width direction of the remaining part is wider than the thickness of the piezoelectric layer and is narrower than the width of the lower electrode.
In the thirty-second aspect, the film thickness of the piezoelectric layer in the width direction thereof becomes substantially uniform and the piezoelectric characteristic is not degraded.
According to a thirty-third aspect of the present invention, in the ink jet recording head of any of the twenty-ninth to thirty-second aspects, an end in a longitudinal direction of the piezoelectric layer is disposed in the proximity of the end portion of the pressure generating chamber where the lower electrode is extended to the top of the peripheral wall and the distance from that end to a part where the lower electrode extended to the outside becomes wider is wider than the thickness of the piezoelectric layer and is narrower than the width of the lower electrode.
In the thirty-third aspect, the film thickness of the piezoelectric layer in the proximity of the end in the longitudinal direction of the pressure generating chamber becomes uniform and if the piezoelectric layer is patterned, the lower electrode therebelow does not become thin.
According to a thirty-fourth aspect of the present invention, in the ink jet recording head of any of the twenty-ninth to thirty-third aspects, the remaining part has a width which is 50% or more of the width of the partition between the adjacent pressure generating chambers.
In the thirty-fourth aspect, the remaining part is formed in a predetermined width, whereby the piezoelectric layer is formed in a uniform film thickness more reliably.
According to a thirty-fifth aspect of the present invention, in the ink jet recording head of any of the twenty-ninth to thirty-fourth aspects, the lower electrode and the remaining part are formed in an area of a width of 50% or more of the area corresponding to the pressure generating chambers placed side by side and the partitions on both sides of the pressure generating chambers in the width direction thereof.
In the thirty-fifth aspect, the lower electrode and the remaining part are set to predetermined dimensions, whereby the film thickness of the piezoelectric layer becomes uniform reliably.
According to a thirty-sixth aspect of the present invention, in the ink jet recording head of any of the twenty-ninth to thirty-third aspects, the lower electrode and the remaining part are formed in an area of 50% or more of all area of the flow passage formation substrate.
In the thirty-sixth aspect, the lower electrode and the remaining part are set to predetermined dimensions, whereby the film thickness of the piezoelectric layer becomes uniform reliably.
According to a thirty-seventh aspect of the present invention, in the ink jet recording head of any of the first to thirty-sixth aspects, the crystalline structure of the piezoelectric layer on the lower electrode is substantially the same as that on the insulating layer.
In the thirty-seventh aspect, the crystalline state of the piezoelectric layer formed on the insulating layer becomes the same as that of the piezoelectric layer formed on the lower electrode, so that cracks do not occur and an abnormal stress does not occur on pattern boundaries either.
According to a thirty-eighth aspect of the present invention, in the ink jet recording head of the thirty-seventh aspect, crystal seed as a nucleus of crystal of the piezoelectric layer is formed on a surface of the insulating layer.
In the thirty-eighth aspect, the crystal structure of the piezoelectric layer is aligned in one orientation and is substantially uniformly formed owing to the crystal seed and occurrence of cracks, etc., is prevented.
According to a thirty-ninth aspect of the present invention, in the ink jet recording head of the thirty-eighth aspect, the crystal seed is formed like islands.
In the thirty-ninth aspect, the crystal of the piezoelectric layer is grown from the crystal seed formed like islands.
According to a fortieth aspect of the present invention, in the ink jet recording head of any of the eighteenth to thirty-ninth aspects, a second insulating layer is provided on the outside of the end of the lower electrode.
In the fortieth aspect, the piezoelectric layer does not become thin in the proximity of the end of the lower electrode and dielectric breakdown of the piezoelectric layer caused by concentration of electric field is prevented.
According to a forty-first aspect of the present invention, in the ink jet recording head of the fortieth aspect, the second insulating layer has substantially the same film thickness as the lower electrode.
In the forty-first aspect, the level difference between the lower electrode and the second insulating layer is small and the piezoelectric layer of a substantially uniform film thickness can be formed thereon.
According to a forty-second aspect of the present invention, in the ink jet recording head of the fortieth or forty-first aspect, the second insulating layer is made of an insulating material different from that of the insulating layer.
In the forty-second aspect, the second insulating layer delivers a function regardless of the type of insulating material.
According to a forty-third aspect of the present invention, in the ink jet recording head of any of the eighteenth to thirty-ninth aspects, a thick film part is provided on the insulating layer on the outside of the end of the lower electrode.
In the forty-third aspect, the piezoelectric layer does not become thin in the proximity of the end of the lower electrode, so that dielectric breakdown of the piezoelectric layer caused by concentration of electric field can be prevented.
According to a forty-fourth aspect of the present invention, in the ink jet recording head of the forty-third aspect, the thick film part has substantially the same film thickness as the lower electrode.
In the forty-fourth aspect, the level difference between the lower electrode and the thick film part is small and the piezoelectric layer of a substantially uniform film thickness can be formed thereon.
According to a forty-fifth aspect of the present invention, in the ink jet recording head of any of the eighteenth to thirty-ninth aspects, a film tapering part where film thickness of the lower electrode is gradually decreased toward the outside of the piezoelectric active part is provided at the end of the lower electrode.
In the forty-fifth aspect, the film tapering part is provided at the end of the lower electrode, thus the piezoelectric layer formed in the proximity of the end of the lower electrode does not become thin and dielectric breakdown in the proximity of the end of the piezoelectric active part is prevented.
According to a forty-sixth aspect of the present invention, in the ink jet recording head of the forty-fifth aspect, the film tapering part forms a slope where the film thickness of the lower electrode is gradually decreased.
In the forty-sixth aspect, the piezoelectric layer is formed along the slope of the film tapering part and the piezoelectric layer at the end of the piezoelectric active part does not become thin.
According to a forty-seventh aspect of the present invention, in the ink jet recording head of the forty-fifth aspect, the film tapering part is a part where the film thickness of the lower electrode is gradually decreased stepwise.
In the forty-seventh aspect, the piezoelectric layer is formed along the form of the film tapering part and becomes substantially the same film thickness as any other portion.
According to a forty-eighth aspect of the present invention, in the ink jet recording head of the forty-fifth aspect, the film tapering part forms a slanting curved surface where the film thickness of the lower electrode is gradually decreased continuously.
In the forty-eighth aspect, the piezoelectric layer is formed along the form of the film tapering part and becomes substantially the same film thickness as any other portion.
According to a forty-ninth aspect of the present invention, in the ink jet recording head of any of the forty-fifth to forty-eighth aspects, a portion of the piezoelectric layer formed on the film tapering part is thicker than any other portion.
In the forty-ninth aspect, concentration of electric field, etc., of the piezoelectric layer in the proximity of the end of the piezoelectric active part does not occur and dielectric breakdown is prevented.
According to a fiftieth aspect of the present invention, in the ink jet recording head of any of the eighteenth to forty-ninth aspects, the other end of the piezoelectric active part has a similar structure to that of the one end thereof.
In the fiftieth aspect, like one end of the piezoelectric active part, the other end is also prevented from being destroyed.
According to a fifty-first aspect of the present invention, in the ink jet recording head of any of the eighteenth to forty-ninth aspects, the other end of the piezoelectric active part is formed by the ends of the piezoelectric layer and the upper electrode and is covered with a discontinuous piezoelectric layer discontinuous with the piezoelectric layer.
In the fifty-first aspect, the end of the piezoelectric active part is protected by the discontinuous piezoelectric layer and the piezoelectric layer and the upper electrode are prevented from peeling, etc.
According to a fifty-second aspect of the present invention, in the ink jet recording head of any of the eighteenth to forty-ninth aspects, the other end of the piezoelectric active part is formed by the ends of the piezoelectric layer and the upper electrode and is fixed with an adhesive.
In the fifty-second aspect, the end of the piezoelectric active part is fixed and the piezoelectric layer and the upper electrode are prevented from peeling, etc.
According to a fifty-third aspect of the present invention, in the ink jet recording head of any of the first to fifty-second aspects, the pressure generating chambers are formed by anisotropic etching and the lower electrode, piezoelectric, and upper electrode layers are formed by film formation and lithography method.
In the fifty-third aspect, ink jet recording heads each having high-density nozzle openings can be manufactured in large quantities and comparatively easily.
According to a fifty-fourth aspect of the present invention, there is provided an ink jet recording apparatus comprising an ink jet recording head of any of the first to fifty-third aspects.
In the fifty-third aspect, an ink jet recording apparatus which is improved in the head drive efficiency and can well jet ink can be provided.